Batteries are common household and industrial power sources familiar to almost everyone and used in a myriad of different low tech to high tech devices and applications. Batteries are used in flashlights, radios, laptop computers, personal medical devices such as hearing aids and insulin pumps, energy storage units for electrical grids and solar energy sources, and vehicles. Batteries may be single use, throwaway batteries, which are used once and discarded, or rechargeable batteries that may repeatedly be charged to store electrical energy and discharged to provide useful electrical current.
A battery comprises at least one, and typically many, energy storage units, referred to as “cells” that are configured to store electrical energy and are controllable to release the energy to provide power. While there are many different types and configurations of cells, many of the most common cells typically comprise an anode and a cathode that sandwich an electrolyte medium between them. During discharge reactions take place in the cell. The cell converts the free energy of cell's reactions into electric energy. During discharge, at the anode a component of the anode is oxidized and at the cathode a component of the cathode is reduced.
If the anode and cathode are not electrically connected so that a current of electrons can flow from the anode to the cathode, a state of equilibrium is reached at which there is no net reaction. A potential difference between the anode and cathode at equilibrium is referred to as an “open circuit voltage (OCV)”.
If on the other hand, the anode and cathode are connected by a conducting element, electrons flow from the anode to the cathode through the conducting element and ions flow through the electrolyte medium. The currents continue to flow until one of the active materials, a component of the anode that is oxidized or a component of the cathode that is reduced, is consumed, or when one of the anode or cathode is blocked by, for example, a discharge product.
If the battery is a single use, one time, throwaway battery, the discharge product cannot be converted (by charging the cell) back to its original components. If the battery is rechargeable, the discharge product or products can be converted back to their respective origins in the anode and cathode. Recharging is performed by driving a current through the battery in a direction opposite to the flow of current during discharging.
State-of-the-art lithium-ion polymer cells are considered to be the best rechargeable cells on the market. They comprise a graphitic-carbon anode and a lithium-intercalated transition-metal-oxide positive electrode. A liquid electrolyte comprising lithium salts dissolved in organic solvents and supported in a microporous-polymer separator is located between the anode and cathode. The theoretical specific energy of lithium-ion polymer battery cells is about 400 to 500 watt-hours/kg (Wh/kg).
Lithium-air cells and other alkali metal-air cells comprising an aqueous electrolyte require a relatively complicated arrangement to isolate the alkali metal from the aqueous electrolyte. US Publication US 2008/0268327, the disclosure of which is incorporated herein by reference, describes alkali metal-air cells comprising an alkali metal anode, an air cathode, an aqueous electrolyte in ionic communication with the cathode and an alkali metal cation conductive membrane that isolates the anode from the aqueous electrolyte.
Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that to the extent any terms are defined in these incorporated documents in a manner that conflicts with the definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered.
The description above is presented as a general overview of related art in this field and should not be construed as an admission that any of the information it contains constitutes prior art against the present patent application.